Influences of Infection and Stress on Cytokine Expression in Blood Samples of Harbour Porpoises (Phocoena phocoena)
Cytokines as mediators of the immune response have been described as indicators of infections and stress. Cytokines are also used to distinguish T-helper cell (Th) subpopulations, which are responsible for the progression of an immune response. To study cytokine expression and to detect changes during infection, we investigated blood samples taken over the course of six months from two harbour porpoises (Phocoena phocoena) living in the Fjord & Belt Centre in Kerteminde (DK). Both animals developed health problems during this period and were occasionally treated with antibiotics. To analyse the influence of stress, we compared cytokine expression in blood samples taken from the two porpoises when they were healthy with those of five wild catches from Danish waters. We analysed expression of pro-inflammatory cytokines, Interleukin-(IL)-1β, IL-2, -6, -8; tumour necrosis factor-(TNF)-α; anti-inflammatory cytokines IL-4, -10; and transforming growth factor-(TGF)-β, using real time RT-PCR. IL-2 was also used as a marker for Th1 cells, IL-4 as a marker for Th2 cells, and TGFβ as a marker for Th3 cells. Both animals living in captivity showed an increase of pro-inflammatory cytokines and the Th1-cytokine IL-2 in three months. In two months a down regulation of cytokine mRNA and an increase of Th2- and Th3-cytokines, IL-4 and TGFβ, was obvious. This suggests the occurrence of inflammatory incidences and appropriate immune responses followed by regulation of excessive immune response or an impairment of the immune system. Comparing the cytokine expression of healthy animals and by-catches revealed an obvious switch to Th2- and Th3-cytokines with down regulation of pro-inflammatory cytokines, which indicates a stress induced suppression of the immune system. The ratio of Th1 to Th2 and Th3 cytokines seems to be helpful to analyse the function of the immune response, the influence of stress and thus the health status of marine mammals.
The authors wish to thank the colleagues from the Fjord and Belt Centre in Kerteminde (Denmark) for the blood samples of the harbour porpoises.